Thermal radiation from a nuclear blast is very intense and can start fires and cause temporary or permanent blindness even at substantial distances from the center of the blast. For example, the thermal radiation could be injurious to the crew of an aircraft in the vicinity of a nuclear blast.
Glass transmits a high percentage of the thermal radiation which is incident upon it, and accordingly, the windows of the aircraft or other structure in the vicinity of the nuclear blast typically provide the greatest radiation leakage path to the interior of the structure. Thermal energy transmission through a window can be substantially reduced by incorporating photochromic dyes and infrared filters into the window. It is known to accomplish this by sandwiching a core of epoxy containing the photochromic dye between glass panels. This laminated structure transmits light in the visible range under normal, or benign, conditions and may be used as a window or laminated to an existing window. When exposure to intense thermal radiation levels in the vicinity of a nuclear blast, the photochromic material undergoes a temporary transformation and blocks the transmittance of much of the thermal radiation.
Although this laminated structure performs its functions well, it is difficult to make. For example, although the core can be cast and cured, it is difficult to retain the glass panels in position during the casting and curing process. This problem increases as the dimensions and mass of the glass panels increase. In addition, the broad surfaces or faces of each of the glass panels must be flat and parallel in order for the laminate to perform its functions properly. Conventional purchased glass panels are typically slightly warped or sufficiently uneven to perform well for this purpose. In addition, casting of the core causes heat transfer to the glass panels and whatever tooling is used to retain them. The glass panels and the tooling typically have different coefficients of expansion, and this further complicates retention of the panels.